Tubulointerstitial disease: role of ischemia and microvascular disease

Risk Factors and Mechanisms Underlying Cross-Shift Decline in Kidney Function in Guatemalan Sugarcane Workers

OBJECTIVE

Identify early biomarkers and mechanisms of acute kidney injury in workers at risk of developing chronic kidney disease of unknown origin (CKDu).

METHODS

We assessed cross-shift changes in kidney function and biomarkers of injury in 105 healthy sugarcane workers. We obtained pre-harvest clinical data as well as daily environmental, clinical, and productivity data for each worker.

RESULTS

The average percent decline in cross-shift estimated glomerular filtration rate (eGFR) was 21.8% (standard deviation [SD] 13.6%). Increasing wet bulb globe temperature (WBGT), high uric acid, decreased urine pH, urinary leukocyte esterase, and serum hyperosmolality were risk factors for decline in kidney function.

CONCLUSIONS

Sugarcane workers with normal kidney function experience recurrent subclinical kidney injury, associated with elevations in biomarkers of injury that suggest exposure to high temperatures and extreme physical demands.

Aristolochic acid inhibits Slit2-induced migration and tube formation via inactivation of Robo1/Robo2-NCK1/NCK2 signaling pathway in human umbilical vein endothelial cells

Robo1/Robo2-NCK1/NCK2 signaling pathway controls endothelial cell sprouting and migration induced by Slit2 or VEGF, but whether it is involved in peritubular capillary (PTC) rarefaction of Aristolochic acid nephropathy (AAN) is unclear. In the present study, we evaluated whether AA exerts antiangiogenic effects by targeting this signaling pathways in HUVECs. HUVECs or lentivirus-mediated NCK1-overexpressing HUVECs were stimulated with AA (1, 2 or 3 μg/ml) in the absence or presence of 6 nM Slit2. Our results showed that AAІ (1-3 μg/ml) dose-dependently inhibited the migration and tube formation of HUVECs. This inhibition was in parallel with down-regulated mRNA and protein expression of Slit2/Robo1/Robo2-NCK1/NCK2 signaling pathway. Importantly, overexpression of NCK1 rescued AAІ-impaired angiogenesis, as evidenced by the increase of cell migration and tube formation of HUVECs in response to Slit2. The down-regulation of NCK2 and decreased activation of Rac1 was also restored by overexpression of NCK1. Taken together, our findings show that AA inhibits Slit2-induced migration and tube formation via inactivation of Robo1/Robo2-NCK1/NCK2 signaling pathway in HUVECs, and NCK1 might be a potential agent for vascular remodeling in AAN and diseases associated with impaired angiogenesis.

Glucofucogalactan, a heterogeneous low-sulfated polysaccharide from Saccharina japonica and its bioactivity

Crude polysaccharide obtained from Saccharina japonica using acid hydrolysis and precipitation was separated into sulfated fuco-oligosaccharide (HDF1) and heteropolysaccharide (HDF2). To further explore the bioactive fraction, HDF2 was successfully separated using membrane filtration into HDF2A and HDF2B, which differed in chemical composition and molecular weight. The bioactivity of all the fractions was tested in vitro, including immunomodulatory activity in RAW 264.7 cells and the protective activity in aristolochic acid (AA)-induced NRK-52E cell injury. HDF1 and HDF2B (low-molecular weight sulfated fucans/fuco-oligosaccharides) did not increase the nitric oxide production in RAW 264.7 cells, whereas HDF2 and HDF2A exhibited potential immunomodulatory activity. All the tested compounds showed different degrees of protective activity in AA-induced injury; HDF2A exhibited superior protective activity. Through chemical analysis, HPLC analysis, and IR spectroscopy and MS, it was determined that HDF2A was a galactose-enriched heteropolysaccharide- glucofucogalactan with a distinctive 2:1 ratio of galactose to fucose. In addition, HDF2A also contained a high amount of glucose and minor amounts of mannose, rhamnose, and xylose, with a low content of sulfate. Thus, HDF2A, a complex heterogeneous polysaccharide mixture with a unique monosaccharide composition, could be studied for further structural characterization and pharmaceutical applications.

Effects of aristolochic acid I and/or hypokalemia on tubular damage in C57BL/6 rat with aristolochic acid nephropathy

BACKGROUND/AIMS

This study was designed to investigate the roles of aristolochic acid I (AA-I) and hypokalemia in acute aristolochic acid nephropathy (AAN).

METHODS

After an adaptation period (1 week), a total of 40 C57BL/6 mice (male, 8 weeks old) were divided into four groups: I (control group), II (low potassium [K] diet), III (normal K diet with administration of AA-I [10 mg/kg weight]), and IV (low K diet with AA-I). After collecting 24 hours of urine at 2 weeks, the mice were sacrificed, and their blood and kidneys were obtained to perform immunochemical staining and/or Western blot analysis.

RESULTS

Proteinuria, glycosuria, and increased fractional excretion of sodium and K were prominent in groups III and IV (p < 0.05). Diffuse swelling and poor staining of collecting duct epithelial cells were evident in the medullas of group II. Typical lesions of toxic acute tubular injury were prominent in the cortices of groups III and IV. Α-Smooth muscle actin (α-SMA) was higher in the cortices of the mice in groups III and IV versus group II (p < 0.05), and higher in the medullas of group IV than groups I and III (p < 0.05). E-cadherin was higher in the cortices of groups III and IV compared to group I (p < 0.05). The F4/80 value was higher in the cortices and medullas of groups II, III, and IV compared to group I (p < 0.05), particularly in the case of group II.

CONCLUSIONS

AA-I can induce acquired Fanconi syndrome in the acute stage of AAN. Macrophages appear to play a key role in the pathogenesis of AAN and hypokalemic nephropathy. It remains uncertain whether hypokalemia plays any role in AAN and hypokalemia.

Vascular homeostasis in early (normo-albuminuric) type 2 diabetic nephropathy

Background: Renal microvascular disease and reduction in peritubular capillary flow are generally observed in type 2 diabetic nephropathy (DN). Earlier therapeutic strategy with vasodilators has improved renal function in normo-albuminuric type 2 DN. Objective: Study the mechanism of vascular homeostasis in twenty patients associated with normo-albuminuric type 2 DN. Results: Angiogenic factors were observed in normo-albuminuric type 2 DN, where vascular endothelial growth factor (VEGF), was 420 ± 341 vs. 428±291 pg/mL (normal), and vascular endothelial growth factor - receptor 1 (VEGF-R1) was 60±12 vs. 49±5 ng/mL (normal), which were not significantly different from the controls. Anti-angiogenic factors were observed in normo-albuminuric type 2 DN, where angiopoietin-2, was 2309+1125 vs. 1671±835 pg/mL (normal), and vascular endothelial growth factor - receptor 2 (VEGF-R2) was 5715±1400 vs.6126 ±1060 ng/mL (normal), which were not significantly different from the controls. Conclusion: The mechanism of vascular homeostasis was adequately functional in normo-albuminuric type 2 DN. This mechanism may explain the positive response to vasodilators and improved renal function in early stage of type 2 DN following the vasodilator treatment.

Retinal Vascular Imaging Markers and Incident Chronic Kidney Disease: A Prospective Cohort Study

Retinal microvascular changes indicating microvascular dysfunction have been shown to be associated with chronic kidney disease (CKD) in cross-sectional studies, but findings were mixed in prospective studies. We aimed to evaluate the relationship between retinal microvascular parameters and incident CKD in an Asian population. We examined 1256 Malay adults aged 40–80 years from the Singapore Malay Eye Study, who attended both the baseline (2004–07) and the follow-up (2011–13) examinations and were free of prevalent CKD. We measured quantitative retinal vascular parameters (arteriolar and venular calibre, tortuosity, fractal dimension and branching angle) using a computer-assisted program (Singapore I Vessel Assessment, SIVA) and retinopathy (qualitative parameter) using the modified Airlie house classification system from baseline retinal photographs. Incident CKD was defined as an estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m² + 25% decrease in eGFR during follow-up. Over a median follow-up period of 6 years, 78 (6.21%) developed CKD (70.5% had diabetes). In multivariable models, smaller retinal arterioles (hazards ratio [95% confidence interval] = 1.34 [1.00–1.78]), larger retinal venules (2.35 [1.12–5.94] and presence of retinopathy (2.54 [1.48–4.36]) were associated with incident CKD. Our findings suggest that retinal microvascular abnormalities may reflect subclinical renal microvascular abnormalities involved in the development of CKD.

The metabolic syndrome and chronic kidney disease

The metabolic syndrome (MetS) is a cluster of cardiovascular risk factors including insulin resistance (IR), dyslipidemia, and hypertension, which may also foster development of chronic kidney disease. The mechanisms of MetS-induced kidney disease are not fully understood. The purpose of this review is to summarize recent discoveries regarding the impact of MetS on the kidney, particularly on the renal microvasculature and cellular mitochondria. Fundamental manifestations of MetS include IR and adipose tissue expansion, the latter promoting chronic inflammation and oxidative stress that exacerbate IR. Those in turn can elicit various kidney injurious events through endothelial dysfunction, activation of the renin-angiotensin-aldosterone system, and adipokine imbalance. Inflammation and IR are also major contributors to microvascular remodeling and podocyte injury. Hence, these events may result in hypertension, albuminuria, and parenchymal damage. In addition, dyslipidemia and excessive nutrient availability may impair mitochondrial function and thereby promote progression of kidney cell damage. Elucidation of the link between MetS and kidney injury may help develop preventative measures and possibly novel therapeutic targets to alleviate and avert development of renal manifestations.

DNA damage-dependent mechanisms of ageing and disease in the macro- and microvasculature

A decline in the function of the macro- and micro-vasculature occurs with ageing. DNA damage also accumulates with ageing, and thus DNA damage and repair have important roles in physiological ageing. Considerable evidence also supports a crucial role for DNA damage in the development and progression of macrovascular disease such as atherosclerosis. These findings support the concept that prolonged exposure to risk factors is a major stimulus for DNA damage within the vasculature, in part via the generation of reactive oxygen species. Genomic instability can directly affect vascular cellular function, leading to cell cycle arrest, apoptosis and premature vascular cell senescence. In contrast, the study of age-related impaired function and DNA damage mechanisms in the microvasculature is limited, although ageing is associated with microvessel endothelial dysfunction. This review examines current knowledge on the role of DNA damage and DNA repair systems in macrovascular disease such as atherosclerosis and microvascular disease. We also discuss the cellular responses to DNA damage to identify possible strategies for prevention and treatment.

Early stage of vascular disease and diabetic kidney disease: an under-recognized entity

Early stage of vascular disease and diabetic kidney disease (DKD stages 1 and 2) has been under-recognized, under common practice worldwide. The lack of sensitive diagnostic marker leads to late diagnosis and a progression of underlying vascular disease associated with chronic renal ischemia, which eventually intensifies the magnitude of DKD damage. Treatment at this late stage fails to correct the renal ischemia, or restore renal function, due to the altered vascular homeostasis associated with an impaired nitric oxide production. In contrast to the above information, early recognition of vascular disease and DKD with sensitive diagnostic markers would be able to implement an effective prevention of progression of vascular disease and DKD. Treatment at early stage under environment favorable for adequate vascular homeostasis is able to correct the renal ischemia and improve the renal function.

Salt Sensitivity in Response to Renal Injury Requires Renal Angiotensin-Converting Enzyme

Recent evidence indicates that salt-sensitive hypertension can result from a subclinical injury that impairs the kidneys' capacity to properly respond to a high-salt diet. However, how this occurs is not well understood. Here, we showed that although previously salt-resistant wild-type mice became salt sensitive after the induction of renal injury with the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester hydrochloride; mice lacking renal angiotensin-converting enzyme, exposed to the same insult, did not become hypertensive when faced with a sodium load. This is because the activity of renal angiotensin-converting enzyme plays a critical role in (1) augmenting the local pool of angiotensin II and (2) the establishment of the antinatriuretic state via modulation of glomerular filtration rate and sodium tubular transport. Thus, this study demonstrates that the presence of renal angiotensin-converting enzyme plays a pivotal role in the development of salt sensitivity in response to renal injury.

A novel therapy to attenuate acute kidney injury and ischemic allograft damage after allogenic kidney transplantation in mice

Ischemia followed by reperfusion contributes to the initial damage to allografts after kidney transplantation (ktx). In this study we tested the hypothesis that a tetrapeptide EA-230 (AQGV), might improve survival and attenuate loss of kidney function in a mouse model of renal ischemia/reperfusion injury (IRI) and ischemia-induced delayed graft function after allogenic kidney transplantation. IRI was induced in male C57Bl/6N mice by transient bilateral renal pedicle clamping for 35 min. Treatment with EA-230 (20–50mg/kg twice daily i.p. for four consecutive days) was initiated 24 hours after IRI when acute kidney injury (AKI) was already established. The treatment resulted in markedly improved survival in a dose dependent manner. Acute tubular injury two days after IRI was diminished and tubular epithelial cell proliferation was significantly enhanced by EA-230 treatment. Furthermore, CTGF up-regulation, a marker of post-ischemic fibrosis, at four weeks after IRI was significantly less in EA-230 treated renal tissue. To learn more about these effects, we measured renal blood flow (RBF) and glomerular filtration rate (GFR) at 28 hours after IRI. EA-230 improved both GFR and RBF significantly. Next, EA-230 treatment was tested in a model of ischemia-induced delayed graft function after allogenic kidney transplantation. The recipients were treated with EA-230 (50 mg/kg) twice daily i.p. which improved renal function and allograft survival by attenuating ischemic allograft damage. In conclusion, EA-230 is a novel and promising therapeutic agent for treating acute kidney injury and preventing IRI-induced post-transplant ischemic allograft injury. Its beneficial effect is associated with improved renal perfusion after IRI and enhanced regeneration of tubular epithelial cells.

Increased risk of end-stage renal disease among hip fracture patients

BACKGROUND

Inflammation-related microvasculr disease, albuminuria, and rapid deterioration of renal function can accelerate the development of end-stage renal disease (ESRD). The role of hip fracture (HFr), a disorder that involves inflammation, in the development of ESRD has not been fully investigated. This study explored whether HFr increases the risk of ESRD.

METHODS

Taiwan National Health Insurance inpatient claims were used to identify 83,550 patients newly diagnosed with HFr from 2000 to 2006, and 83,550 age- and sex-matched patients without HFr were randomly selected for comparison. Hazards of ESRD combined with HFr, comorbidities, including hypertension, hyperlipidemia, peripheral arterial disease, osteoporosis and asthma, and general health status, with Charlson comorbidity index (CCI), were assessed using data to the end of 2011.

RESULTS

ESRD risk was 1.42-fold higher (95% confidence interval [CI]:1.29-1.33) in the HFr cohort than in the control group, which was computed using the Cox proportional model. Age-specific analysis revealed that the adjusted hazard ratios (aHRs) of ESRD for HFr patients increased slightly as age increased, with an aHR of 1.56 (95% CI:1.35-1.81) for patients 65-74 years old, which gradually decreased to 0.88 (95% CI:0.66-1.18) for patients ≥ 85 years old. ESRD risk increased as HFr severity increased, with an aHR of 6.71 (95% CI:5.90-7.63) for patients with severe HFr.

CONCLUSION

This study is the first to report that HFr, in combination with underlying osteoporosis-related chronic illness, microvascular disease and chronic inflammation, is associated with an increased risk of ESRD, particularly among relatively younger people.

Metabolic syndrome and chronic kidney disease: Current status and future directions

Metabolic syndrome (MetS) is a term used to denote a combination of selected, widely prevalent cardiovascular disease (CVD)-related risk factors. Despite the ambiguous definition of MetS, it has been clearly associated with chronic kidney disease markers including reduced glomerular filtration rate, proteinuria and/or microalbuminuria, and histopathological markers such as tubular atrophy and interstitial fibrosis. However, the etiological role of MetS in chronic kidney disease (CKD) is less clear. The relationship between MetS and CKD is complex and bidirectional, and so is best understood when CKD is viewed as a common progressive illness along the course of which MetS, another common disease, may intervene and contribute. Possible mechanisms of renal injury include insulin resistance and oxidative stress, increased proinflammatory cytokine production, increased connective tissue growth and profibrotic factor production, increased microvascular injury, and renal ischemia. MetS also portends a higher CVD risk at all stages of CKD from early renal insufficiency to end-stage renal disease. Clinical interventions for MetS in the presence of CKD should include a combination of weight reduction, appropriate dietary modification and increase physical activity, plus targeting of individual CVD-related risk factors such as dysglycemia, hypertension, and dyslipidemia while conforming to relevant national societal guidelines.

Cyclodextrin curcumin formulation improves outcome in a preclinical pig model of marginal kidney transplantation

Decreasing organ quality is prompting research toward new methods to alleviate ischemia reperfusion injury (IRI). Oxidative stress and nuclear factor kappa beta (NF-κB) activation are well-described elements of IRI. We added cyclodextrin-complexed curcumin (CDC), a potent antioxidant and NF-κB inhibitor, to University of Wisconsin (UW) solution (Belzer's Solution, Viaspan), one of the most effective clinically approved preservative solutions. The effects of CDC were evaluated on pig endothelial cells and in an autologous donation after circulatory death (DCD) kidney transplantation model in large white pigs. CDC allowed rapid and lasting uptake of curcumin into cells. In vitro, CDC decreased mitochondrial loss of function, improved viability and lowered endothelial activation. In vivo, CDC improved function recovery, lowered histological injury and doubled animal survival (83.3% vs. 41.7%). At 3 months, immunohistochemical staining for epithelial-to-mesenchymal transition (EMT) and fibrosis markers was intense in UW grafts while it remained limited in the UW + CDC group. Transcriptional analysis showed that CDC treatment protected against up-regulation of several pathophysiological pathways leading to inflammation, EMT and fibrosis. Thus, use of CDC in a preclinical transplantation model with stringent IRI rescued kidney grafts from an unfavorable prognosis. As curcumin has proved well tolerated and nontoxic, this strategy shows promise for translation to the clinic.

Role of warm ischemia on innate and adaptive responses in a preclinical renal auto-transplanted porcine model

Background

Deceased after cardiac arrest donor are an additional source of kidney graft to overcome graft shortage. Deciphering the respective role of renal warm and cold ischemia is of pivotal interest in the transplantation process.

Methods

Using a preclinical pig model of renal auto-transplantation, we investigated the consequences of warm and cold ischemia on early innate and adaptive responses as well as graft outcome. Kidneys were subjected to either 60 min-warm ischemia (WI) or auto-transplanted after cold storage for 24 h at 4°C (CS), or both conditions combined (WI + CS). Renal function, immune response and cytokine expression, oxidative stress and cell death were investigated at 3 h, 3 and 7 days (H3, D3 and D7) after reperfusion. At 3 months, we focused on cell infiltration and tissue remodelling.

Results

WI + CS induced a delayed graft function linked to higher tubular damage. Innate response occurred at D3 associated to a pro-oxidative milieu with a level dependent on the severity of ischemic injury whereas adaptive immune response occurred only at D7 mainly due to CS injuries and aggravated by WI. Graft cellular death was an early event detected at H3 and seems to be one of the first ischemia reperfusion injuries. These early injuries affect graft outcome on renal function, cells infiltration and fibrosis development.

Conclusions

The results indicate that the severe ischemic insult found in kidneys from deceased after cardiac arrest donor affects kidney outcome and promotes an uncontrolled deleterious innate and adaptive response not inhibited 3 months after reperfusion.

Urgent call for reconsideration of chronic kidney disease

Circulating toxins namely: free radicals, cytokines and metabolic products induce glomerular endothelial dysfunction, hemodynamic maladjustment and chronic ischemic state;this leads to tubulointerstitial fibrosis in chronic kidney disease (CKD). Altered vascular homeostasis observed in late stage CKD revealed defective angiogenesis and impaired nitric oxide production explaining therapeutic resistance to vasodilator treatment in late stage CKD. Under current practice, CKD patients are diagnosed and treated at a rather late stage due to the lack of sensitivity of the diagnostic markers available. This suggests the need for an alternative therapeutic strategy implementing the therapeutic approach at an early stage. This view is supported by the normal or mildly impaired vascular homeostasis observed in early stage CKD. Treatment at this early stage can potentially enhance renal perfusion, correct the renal ischemic state and restore renal function. Thus, this alternative therapeutic approach would effectively prevent end-stage renal disease.

Microvascular dilatation after haemodialysis is determined by the volume of fluid removed and fall in mean arterial pressure

BACKGROUND/AIMS

The effects of haemodialysis on the microcirculation are poorly understood. This study examined the changes in small vessel calibre.

METHODS

24 patients (including 12 males, median age 62.5 years, range 30-87) underwent digital retinal photography immediately before and after routine haemodialysis. Arteriolar and venular calibres were measured from the images by a trained grader using a highly reproducible, computer-assisted method.

RESULTS

Patients had an average 2.0 ± 0.3 litres of fluid removed with dialysis, and their mean arterial blood pressure fell by 6.8 mm Hg (CI 13.8-0.2, p = 0.06). Retinal arteriole calibre did not change (mean difference 2.3 µm, CI -1.1 to 5.7, p = 0.17) but the venules dilated (mean difference 12.7 µm, CI 7.3-18.3, p < 0.001). Calibre returned to baseline by 2 h. Venules dilated less in diabetics than non-diabetics (mean difference -6.2 µm, CI -9.6 to -2.9, p < 0.01). Retinal venular dilatation correlated positively with the volume of fluid removed per kilogramme body weight (5.9, CI 0.2-11.5, p = 0.04), and negatively with the fall in mean arterial pressure (-0.36, CI -0.72 to -0.01, p < 0.05) after adjusting for age, gender, diabetes and dyslipidaemia.

CONCLUSION

Haemodialysis is associated with systemic venular dilatation.

Change of Cyclosporine Absorption over the Time after Kidney Transplantation

Background

Although the immunosuppressant cyclosporine (CsA) is widely used after kidney transplantation over the long term, there is still no firm consensus on the best way to monitor of CsA blood levels.

Objectives

Cyclosporine (CsA) assay is critical for the management of renal transplant recipients due to inter– and intra–patient variation in CsA absorption and metabolism. Patients and Methods: In a retrospective cross sectional study, blood levels of CsA (through and 2 hours post dose) measured at least 5 times during 3 years post transplantation, in 7702 kidney transplant recipients from different transplant center of Tehran, IR Iran between 2008 and 2012. Cyclosporine absorption (CA) calculated C2/C0 ratio.

Results

CA had a significant correlation with allograft function (P = 0.000, r =.0.285), this correlation was stronger than its relationship with C0 and C2 blood levels (P = 0.000 and P = 0.000 as well as r = 0.033 and r = 0.090, respectively). In univariate analysis during different times after transplantation, C0 and C2 blood levels significantly decreased over three years follow up (P = 0.000), (P = 0.000); While, CA reversely increases over the time (P = 0.000). In linear regression model overall CA levels had correlation with lower age of recipient (P = 0.02), hypokalemia (P = 0.001), higher level of creatinine (P = 0.02) and triglyceride (P = 0.001).

Conclusions

The present study shows that CsA absorption changes trough the post-transplant time and appears to increases over time in long–term period after kidney transplantation.

Magnetic resonance elastography of the kidneys: feasibility and reproducibility in young healthy adults

PURPOSE

To evaluate the feasibility and reproducibility of renal magnetic resonance elastography (MRE) in young healthy volunteers.

MATERIALS AND METHODS

Ten volunteers underwent renal MRE twice at a 4-5 week interval. The vibrations (45 and 76 Hz) were generated by a speaker positioned beneath the volunteers' back and centered on their left kidney. For each frequency, three sagittal slices were acquired (eight phase offsets per cycle, motion-encoding gradients successively positioned along the three directions of space). Shear velocity images were reconstructed using the curl operator combined with the local frequency estimation (LFE) algorithm.

RESULTS

The mean shear velocities measured in the renal parenchyma during the two examinations were not significantly different and exhibited a mean variation of 6% at 45 Hz and 76 Hz. The mean shear velocities in renal parenchyma were 2.21 ± 0.14 m/s at 45 Hz (shear modulus of 4.9 ± 0.5 kPa) and 3.07 ± 0.17 m/s at 76 Hz (9.4 ± 0.8 kPa, P < 0.01). The mean shear velocities in the renal cortex and medulla were respectively 2.19 ± 0.13 m/s and 2.32 ± 0.16 m/s at 45 Hz (P = 0.002) and 3.06 ± 0.16 m/s and 3.10 ± 0.22 m/s at 76 Hz (P = 0.13).

CONCLUSION

Renal MRE was feasible and reproducible. Two independent measurements of shear velocities in the renal parenchyma of the same subjects showed an average variability of 6%.

Idiopathic Recurrent Calcium Urolithiasis (IRCU): pathophysiology evaluated in light of oxidative metabolism, without and with variation of several biomarkers in fasting urine and plasma--a comparison of stone-free and -bearing male patients, emphasizing mineral, acid-base, blood pressure and protein status

BACKGROUND

IRCU is traditionally considered as life?style disease (associations with, among others, overweight, obesity, hypertension, type-2 diabetes), arising from excess, in 24 h urine, of calcium (Ca) salts (calcium oxalate (CaOx), calcium phosphate (CaPi)), supersaturation of, and crystallization in, tubular fluid and urine, causing crystal-induced epithelial cell damage, proteinuria, crystal aggregation and uroliths.

METHODS

Another picture emerges from the present uncontrolled study of 154 male adult IRCU patients (75 stone-bearing (SB) and 79 age-matched stone-free (SF)), in whom stone-forming and other parameters in fasting urine and plasma were contrasted with five biomarkers (see footnote) of oxidative metabolism (OM), without and with variation of markers.

RESULTS

1) In SB vs. SF unstratified OM biomarkers were statistically unchanged, but the majority of patients was overweight; despite, in SB vs. SF urine pH, total and non-albumin protein concentration were elevated, fractional urinary uric acid excretion and blood bicarbonate decreased, whereas urine volume, sodium, supersaturation with CaOx and CaPi (as hydroxyapatite) were unchanged; 2) upon variation of OM markers (strata below and above median) numerous stone parameters differed significantly, among others urine volume, total protein, Ca/Pi ratio, pH, sodium, potassium, plasma Ca/Pi ratio and parathyroid hormone, blood pressure, renal excretion of non-albumin protein and other substances; 3) a significant shift from SF to SB patients occurred with increase of urine pH, decrease of blood bicarbonate, and increase of diastolic blood pressure, whereas increase of plasma uric acid impacted only marginally; 4) in both SF and SB patients a strong curvilinear relationship links a rise of urine Ca/Pi to urine Ca/Pi divided by plasma Ca/Pi, but in SB urine Ca/Pi failed to correlate significantly with urine hydroxyapatite supersaturation; 5) also in SB, plasma Ca/Pi and urinary nitrate were negatively correlated, whereas in SF plasma Ca/Pi ratio, PTH and body mass index correlated positively; 6) multivariate regression analysis revealed that PTH, body mass index and nitrate together could explain 22 (p = 0.002) and only 7 (p = 0.06) per cent of variation of plasma Ca/Pi in SF and SB, respectively.

CONCLUSIONS

In IRCU a) numerous constituents of fasting urine, plasma, blood and blood pressure change in response to variation of OM biomarkers, suggesting involvement of OM imbalance as factor in functional deterioration of tissue; b) in the majority of patients a positive exponential relationship links urine Ca/Pi to urine Ca/Pi divided by plasma Ca/Pi, presumably to accumulate Ca outside tubular lumen, thereby minimizing intratubular and urinary Ca salt crystallization; c) alteration of interactions of low urine nitrate, PTH and Ca/Pi in plasma may be of importance in formation of new Ca stone and co-regulation of dynamics of blood vasculature; d) overweight, combined with OM-modified renal interstitial environment appears to facilitate these processes, carrying the risk that CaPi mineral develops within or/and close to blood vessel tissue, and spreads towards urothelium. - For future research focussing on IRCU pathogenesis studies are recommended on the role of affluent lifestyle mediated renal ischemia, mild hypertensive nephropathy, rise of uric acid precursor oxypurines and uricemia, clarifying also why loss of significance of interrelationships of OM biomarkers with traditional Ca stone risk factors is characteristic for SB patients.

The microvasculature in chronic kidney disease

BACKGROUND AND OBJECTIVES

Individuals with chronic kidney disease (CKD) stages 3 to 5 have an increased risk of cardiac and other vascular disease. Here we examined the association of CKD 3 to 5 with small vessel caliber.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a cross-sectional observational study of 126 patients with CKD stages 3 to 5 (estimated GFR [eGFR] <60 ml/min per 1.73 m(2)) and 126 age- and gender-matched hospital patients with CKD 1 or 2. Retinal vessel diameters were measured from digital fundus images by a trained grader using a computer-assisted method and summarized as the central retinal artery equivalent (CRAE) and central retinal vein equivalent (CRVE).

RESULTS

Patients with CKD 3 to 5 had a smaller mean CRAE and CRVE than hospital controls (139.4 ± 17.8 μm versus 148.5 ± 16.0 μm, P < 0.001; and 205.0 ± 30.7 μm versus 217.4 ± 25.8 μm, respectively; P = 0.001). CRAE and CRVE decreased progressively with each stage of renal failure CKD1-2 to 5 (P for trend = 0.08 and 0.04, respectively). CKD and hypertension were independent determinants of arteriolar narrowing after adjusting for age, gender, diabetes, dyslipidemia, and smoking history. Patients with CKD 5 and diabetes had a larger mean CRAE and CRVE than nondiabetics (141.4 ± 14.9 μm versus 132.9 ± 14.2 μm; 211.1 ± 34.4 μm versus 194.8 ± 23.8 μm).

CONCLUSIONS

The microvasculature is narrowed in patients with reduced eGFR.

Preservation strategies to reduce ischemic injury in kidney transplantation: pharmacological and genetic approaches

PURPOSE OF REVIEW

In the current graft shortage, it is paramount to improve the quality of transplanted organs. Organ preservation represents an underused therapeutic window with great potential to reduce ischaemia-reperfusion injury (IRI) and improve graft quality. Herein, we review strategies using this window as well as other promising work targeting IRI pathways using pharmacological treatments and gene therapy.

RECENT FINDINGS

We highlight studies using molecules administered during kidney preservation to target key components of IRI such as inflammation, oxidative stress, mitochondrial activity and the coagulation pathway. We further expose recent studies of gene therapy directed against inflammation or apoptosis during cold storage. Other pathways with potential therapeutic molecules are cited.

SUMMARY

The use of cold preservation as a therapeutic window to deliver pharmacological or gene therapy treatments can significantly improve both short-term and long-term graft outcomes. Even if human gene therapy remains hampered by the quantity of agent needed and the potential harmfulness of the vector, it clearly offers a wide array of possibilities for the future. Although gene therapy is still too immature, we expose pharmacological strategies which can readily be applied to the clinic and improve both transplantation success rates and the patients' quality of life.

Capillary rarefaction, hypoxia, VEGF and angiogenesis in chronic renal disease

Tubulointerstitial hypoxia and peritubular capillary rarefaction are typical features of chronic progressive renal disease. In response to low oxygen supply, hypoxia-inducible factors (HIFs) are activated but until now, it is unclear if this increased expression leads to a stabilization of the disease process and thus is nephroprotective or contributes to interstitial fibrosis and/or tubular atrophy. This duality has also been described as far as vascular endothelial growth factor (VEGF), one of the major target genes of HIFs, is concerned. On the one hand, neoangiogenesis driven by VEGF, if intact, ameliorates hypoxia, on the other, VEGF is a potent pro-inflammatory mediator and neoangiogenesis, if defective because interference by other pathologies exaggerates injury. In summary, experimental data support the idea that dependent on timing and predominant pathology, hypoxia counter-regulatory factors exert beneficial or undesirable effects. Thus, before their therapeutic potential can be fully explored, a better way to characterize the clinical and pathophysiological situation in an individual patient is mandatory.

Renal injury in angiotensin II+L-NAME-induced hypertensive rats is independent of elevated blood pressure

The balance between angiotensin II (ANG II) and nitric oxide plays an important role in renal function and is thought to contribute to the progression of renal injury in experimental hypertension. In the present study, we investigated the extent of blood pressure (BP)-dependent and BP-independent pathways of renal injury following 2 wk of hypertension produced by intravenous infusion of ANG II (5 ng·kg⁻¹·min⁻¹)+N(ω)-nitro-l-arginine methyl ester (l-NAME; 1.4 μg·kg⁻¹·min⁻¹) in male Sprague-Dawley rats. An aortic balloon occluder was positioned between the renal arteries to maintain (24 h/day) BP to the left kidney (servo-controlled) at baseline levels, whereas the right kidney (uncontrolled) was chronically exposed to elevated BP. Over the 14-day experimental protocol, the average BP to uncontrolled kidneys (152.7 ± 1.8 mmHg) was significantly elevated compared with servo-controlled (113.0 ± 0.2 mmHg) kidneys and kidneys from sham rats (108.3 ± 0.1 mmHg). ANG II+l-NAME infusion led to renal injury that was focal in nature and mainly confined to the outer medulla. Despite the differences in BP between servo-controlled and uncontrolled kidneys, there was a similar ~3.5-fold increase in renal outer medullary tubular injury, ~2-fold increase in outer medullary interstitial fibrosis, ~2-fold increase in outer medullary macrophage infiltration, and a significant increase in renal oxidative stress, all of which are indicative of BP-independent mediated pathways. The results of this study have important implications regarding the pathogenesis of renal injury in various experimental models of hypertension and provide novel insights regarding the variable association observed between hypertension and renal injury in some human populations.

Hypertension and angiogenesis in the aging kidney: a review

With advanced aging, main components of the kidney are altered, including blood vessels, glomeruli and tubulointerstitium. Disruption in these 3 elements is interconnected and associated with several modifications, such as loss of kidney mass and systemic, metabolic and immunologic diseases. In this review we focus on renal blood vessels, the key role of hypertension and angiogenesis in the elderly kidney, the hemodynamic and molecular mechanisms underlying this aging process and the main factors involved. So far, the present data suggests a strong association between renal disease and hypertension and the impairment of regulatory mechanisms, such as angiogenesis in the aging kidney. The endothelium is a key player in vascular control and appears to be also disrupted in many compensatory functions (i.e., vasodilation). Perspectives for the management of the dysfunctional aging kidney are also addressed.

New and improved strategies for the treatment of gout

The Western world appears to be in the midst of the third great gout epidemic of all time. In this century, gout is increasing in prevalence despite an increased understanding of its risk factors and pathophysiology, and the availability of reasonably effective treatment. The main cultural factors responsible for this appear to be diet, obesity, ethanol use and medications. Excess fructose consumption is a newly recognized modifiable risk factor. The debate has been renewed concerning hyperuricemia as an independent risk factor for renal insufficiency and cardiovascular disease. Prevention is still rooted in lifestyle choices. Existing treatments have proven to be unsatisfactory in many patients with comorbidities. New treatments are available today and on the horizon for tomorrow, which offer a better quality of life for gout sufferers. These include febuxostat, a nonpurine inhibitor of xanthine oxidase with a potentially better combination of efficacy and safety than allopurinol, and investigational inhibitors of URAT-1, an anion exchanger in the proximal tubule that is critical for uric acid homeostasis. New abortive treatments include interleukin-1 antagonists that can cut short the acute attack in 1 to 2 days in persons who cannot take nonsteroidal anti-inflammatory drugs, colchicine or corticosteroids. Lastly, newer formulations of uricase have the ability to dissolve destructive tophi over weeks or months in patients who cannot use currently available hypouricemic agents. Diagnostically, ultrasound and magnetic resonance imaging offer advanced ways to diagnose gout noninvasively, and just as importantly, a way to follow the progress of tophus dissolution. The close association of hyperuricemia with metabolic syndrome, hypertension and renal insufficiency ensures that nephrologists will see increasing numbers of gout-afflicted patients.

Early atherosclerosis aggravates the effect of renal artery stenosis on the swine kidney

Atherosclerotic renal artery stenosis (ARAS) is increasingly identified in patients with end-stage renal disease. Renal function in ARAS patients deteriorates more frequently than in nonatherosclerotic renal artery stenosis (RAS). This study was designed to test the hypothesis that atherosclerosis modifies the relationship between single-kidney hemodynamics and function and the severity of stenosis. The degree of unilateral RAS in domestic pigs (4 normal, 26 RAS, and 22 ARAS) was correlated with renal function and hemodynamics evaluated by 64-slice multidetector computerized tomography before and after endothelium-dependent challenge with ACh. The degree of stenosis and increase in mean arterial pressure were similar in RAS and ARAS. Stenotic single-kidney volume, blood flow, glomerular filtration rate, and cortical perfusion were lower than normal in both RAS and ARAS, but only in RAS correlated inversely with increasing degree of stenosis (r = -0.62, r = -0.49, r = -0.51, and r = -0.46, respectively, P < 0.05 for all). Basal tubular fluid concentration capacity and stenotic cortical perfusion response to ACh were both blunted only in ARAS. This study shows that atherosclerosis modulates the impact of a stenosis in the renal artery on stenotic kidney hemodynamics, function, and tubular dynamics. These observations underscore the direct intrarenal effect of atherogenic factors on the kidneys.

A mildly altered vascular homeostasis in early stage of CKD

BACKGROUND

A continuous increase in number of CKD patients entering ESRD is a growing public health threat, which reflects the present therapeutic failure usually initiating at the late stage of CKD.

OBJECTIVE

To study the mechanism of vascular repair in CKD patients associated with mildly impaired renal function, which included angiogenic factors such as VEFG, angiopoietin-1, and flt-1 (VEGFR1); and antiangiogenic factors such as angiopoietin-2 and KDR (VEGFR2).

RESULTS

A mild defect in angiogenic factor-namely, angiopoietin-1-was observed, whereas VEGF and flt-1 (VEGFR1) were within normal limit. Also, antiangiogenic factor-namely, angiopoietin-2-was mildly elevated, whereas KDR (VEGFR2) remained within normal limit.

CONCLUSION

The mechanism of vascular repair appears to be adequately functional in the early stage of CKD. Therapeutic intervention at this stage can improve renal perfusion and restore renal function as indicated in normoalbuminuric, type 2 diabetic nephropathy. The authors encourage changing the conceptual view of treatment under common treatment at late stage of CKD to treatment at early stage of CKD under an environment favorable for renal regeneration.

Postobstructive regeneration of kidney is derailed when surge in renal stem cells during course of unilateral ureteral obstruction is halted

Unilateral ureteral obstruction (UUO), a model of tubulointerstitial scarring (TIS), has a propensity toward regeneration of renal parenchyma after release of obstruction (RUUO). No information exists on the contribution of stem cells to this process. We performed UUO in FVB/N mice, reversed it after 10 days, and examined kidneys 3 wk after RUUO. UUO resulted in attenuation of renal parenchyma. FACS analysis of endothelial progenitor (EPC), mesenchymal stem (MSC) and hematopoietic stem (HSC) cells obtained from UUO kidneys by collagenase-dispersed single-cell suspension showed significant increase in EPC, MSC, and HSC compared with control. After RUUO cortical parenchyma was nearly restored, and TIS score improved by 3 wk. This reversal process was associated with return of stem cells toward baseline level. When animals were chronically treated with nitric oxide synthase (NOS) inhibitor at a dose that did not induce hypertension but resulted in endothelial dysfunction, TIS scores were not different from control UUO, but EPC number in the kidney decreased significantly; however, parenchymal regeneration in these mice was similar to control. Blockade of CXCR4-mediated engraftment resulted in dramatic worsening of UUO and RUUO. Similar results were obtained in caveolin-1-deficient but not -overexpressing mice, reflecting the fact that activation of CXCR4 occurs in caveolae. The present data show increase in EPC, HSC, and MSC population during UUO and a tendency for these cells to decrease to control level during RUUO. These processes are minimally affected by chronic NOS inhibition. Blockade of CXCR4-stromal cell-derived factor-1 (SDF-1) interaction by AMD3100 or caveolin-1 deficiency significantly reduced the UUO-associated surge in stem cells and prevented parenchymal regeneration after RUUO. We conclude that the surge in stem cell accumulation during UUO is a prerequisite for regeneration of renal parenchyma.

Kidney pathological changes in metabolic syndrome: a cross-sectional study

BACKGROUND

The worldwide prevalence of metabolic syndrome is increasing and has been associated with chronic kidney disease. Kidney pathological findings in patients with metabolic syndrome have not been well described, as was explored in this study.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

We retrospectively screened clinical information for 146 patients who underwent elective nephrectomy for renal cell carcinoma between January 2005 and March 2007 at Brigham and Women's Hospital, Boston, MA. Twelve patients with metabolic syndrome were identified. Twelve age- and sex-matched patients who did not have any of the criteria for metabolic syndrome were used as controls.

PREDICTOR

Presence of metabolic syndrome defined by using Adult Treatment Panel III criteria.

OUTCOMES

Histological characteristics in each group, decrease in kidney function at 1-year follow-up.

MEASUREMENTS

Two pathologists blinded to the clinical diagnosis independently evaluated nephrectomy specimens using Banff criteria to objectively assess histological characteristics.

RESULTS

Baseline characteristics were similar between the 2 groups. On histopathologic examination, patients with metabolic syndrome compared with controls had a greater prevalence of tubular atrophy (P = 0.006), interstitial fibrosis (P = 0.001), and arterial sclerosis (P = 0.001), suggesting microvascular disease. Patients with metabolic syndrome had greater global (P = 0.04) and segmental glomerulosclerosis (P = 0.05). Glomerular volume and cross-sectional surface area were not different. The combined end point of tubular atrophy greater than 5%, interstitial fibrosis greater than 5%, and presence of arterial sclerosis was more prevalent in patients with metabolic syndrome (P = 0.003; odds ratio, 33; confidence interval, 2.9 to 374.3) than controls. After 1 year, estimated glomerular filtration rate was significantly lower in patients with metabolic syndrome compared with controls (P = 0.03).

LIMITATIONS

Small sample size, retrospective design.

CONCLUSIONS

We report a high prevalence of microvascular disease in patients with metabolic syndrome. There was a steeper decrease in kidney function over time in patients with metabolic syndrome, suggesting limited renal reserve. Aggressive screening and management may be warranted in patients with metabolic syndrome to protect kidney function.

Retinal microvascular caliber and chronic kidney disease in an Asian population

Retinal arteriolar narrowing is a marker of microvascular damage from elevated blood pressure. Between August 2004 and June 2006, the authors examined the association between retinal vascular diameter and chronic kidney disease in a population-based cohort of 3,280 community-dwelling adults of Malay ethnicity aged 40-80 years living in Singapore. Chronic kidney disease was defined as 1) an estimated glomerular filtration rate (eGFR) of <60 mL/minute/1.73 m(2) from serum creatinine or 2) the presence of micro/macroalbuminuria defined as urinary albumin:creatinine ratios of > or = 17 mg/g for men and > or = 25 mg/g for women. Retinal arteriolar and venular diameters were measured and summarized as central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE). Individuals with reduced CRAE were more likely to have chronic kidney disease than those with increased CRAE. After controlling for age, gender, education, smoking, diabetes, hypertension, body mass index, and total and high density lipoprotein cholesterol, the authors found the odds ratio comparing the smallest with the largest CRAE quartile to be 1.42 (95% confidence interval: 1.03, 1.96; P(trend) = 0.02) for eGFR of <60 mL/minute/1.73 m(2) and 1.80 (95% confidence interval: 1.11, 2.91; P(trend) = 0.01) for micro/macroalbuminuria. Retinopathy was also found to be positively associated with both eGFR and micro/macroalbuminuria. Retinal venular diameter was not associated with chronic kidney disease. These data suggest that retinal arteriolar narrowing is associated with chronic kidney disease, independent of diabetes and hypertension.

Peritubular capillaries are rarefied in congenital nephrotic syndrome of the Finnish type

Congenital nephrotic syndrome of the Finnish type (NPHS1) is associated with the rapid development of glomerular and tubulointerstitial fibrosis. Here we measured morphologic and molecular changes in the peritubular capillaries of the kidney in patients with NPHS1. Immunohistochemical analysis for the endothelial cell marker CD31 showed marked narrowing and a moderate but significant reduction in peritubular capillary density, especially in areas of increased collagen I and alpha-smooth muscle actin content. No evidence of endothelial-mesenchymal transformation was found. There was increased expression (up to 43-fold) of hypoxia inducible factor-1alpha suggesting tubulointerstitial hypoxia. Double-labeling for CD31 and vimentin showed small foci of peritubular capillary loss and tubular cell damage. While the amount of intercellular adhesion molecule-1 was upregulated in endothelial cells, other adhesion molecules were only modestly expressed. Vascular endothelial growth factor expression was reduced by up to half and decreased endothelial progenitor cell marker CD34 expression indicated lack of vascular repair. Our results suggest that hypoxia in the tubulointerstitium caused by hypoperfusion of glomerular and tubulointerstitial capillaries and rarefaction of the latter may be important for the rapid progression of fibrosis in the kidneys of patients with NPHS1.

Isolation and primary culture of human proximal tubule cells

Primary cultures of renal proximal tubule cells (PTC) have been widely used to investigate tubule cell function. They provide a model system where confounding influences of renal haemodynamics, cell heterogeneity, and neural activity are eliminated. Additionally they are likely to more closely resemble PTC in vivo than established kidney cell lines, which are often virally immortalised and are of uncertain origin. This chapter describes a method used in our laboratories to isolate and culture pure populations of human PTC. The cortex is dissected away from the medulla and minced finely. Following collagenase digestion, the cells are passed through a sieve and separated on a Percoll density gradient. An almost pure population of tubule fragments form a band at the base of the gradient. Cultured in a hormonally defined serum-free growth media, they form a tightly packed monolayer that retains the differentiated characteristics of PTC for up to three passages.

Chronic kidney disease at high altitude

With a prevalence of 10 to 11% in the general population, it is likely that many patients with chronic kidney disease will visit or reside in mountainous areas. Little is known, however, about whether short- or long-duration, high-altitude exposure poses a risk in this patient population. Given that many areas of the kidney are marginally oxygenated even at sea level and that kidney disease may result in further renal hypoxia and hypoxia-associated renal injury, there is concern that high altitude may accelerate the progression of chronic kidney disease. In this review, we address how chronic kidney disease and its management is affected at high altitude. We postulate that arterial hypoxemia at high altitude poses a risk of faster disease progression in those with preexisting kidney disease. In addition, we consider the risks of developing acute altitude illness in patients with chronic kidney disease and the appropriate use of medications for the prevention and treatment of these problems.

Indolent course of tubulointerstitial disease in a mouse model of subpressor, low-dose nitric oxide synthase inhibition

Deficiency of nitric oxide (NO) represents a consistent manifestation of endothelial dysfunction (ECD), and the accumulation of asymmetric dimethylarginine occurs early in renal disease. Here, we confirmed in vitro and in vivo the previous finding that a fragment of collagen XVIII, endostatin, was upregulated by chronic inhibition of NO production and sought to support a hypothesis that primary ECD contributes to nephrosclerosis in the absence of other profibrotic factors. To emulate more closely the indolent course of ECD, the study was expanded to an in vivo model with N(G)-monomethyl-L-arginine (L-NMMA; mimics effects of asymmetric dimethylarginine) administered to mice in the drinking water at subpressor doses of 0.3 and 0.8 mg/ml for 3-6 mo. This resulted in subtle but significant morphological alterations detected in kidneys of mice chronically treated with L-NMMA: 1) consistent perivascular expansion of interstitial matrix components at the inner stripe of the outer medulla and 2) collagen XVIII/endostatin abundance. Ultrastructural abnormalities were detected in L-NMMA-treated mice: 1) increased activity of the interstitial fibroblasts; 2) occasional detachment of endothelial cells from the basement membrane; 3) splitting of the vascular basement membrane; 4) focal fibrosis; and 5) accumulation of lipofuscin by interstitial fibroblasts. Preembedding labeling of microvasculature with anti-CD31 antibodies showed infiltrating leukocytes and agglomerating platelets attaching to the visibly intact or denuded capillaries. Collectively, the data indicate that the mouse model of subpressor chronic administration of L-NMMA is not a robust one (endothelial pathology visible only ultrastructurally), and yet it closely resembles the natural progression of endothelial dysfunction, microvascular abnormalities, and associated tubulointerstitial scarring.

Early detection of acute kidney injury: emerging new biomarkers

Acute kidney injury (AKI) has recently become the preferred term to describe the syndrome of acute renal failure (ARF) with 'failure' or 'ARF' restricted to patients who have AKI and need renal replacement therapy.(1) This allows capture of the broader clinical spectrum of modest reductions in creatinine, which are themselves known to be associated with major increases in both short- and long-term mortality risk.(2-5) It is hoped that this change in nomenclature will facilitate an expansion of our understanding of the underlying pathophysiology and also facilitate definitions of AKI, which allow comparisons among clinical trials of patients with similar duration and severity of illness. This review will cover the need for early detection of AKI and the role of urinary and plasma biomarkers, including enzymuria. The primary message is that use of existing criteria to diagnose AKI, namely elevation of the serum creatinine with or without oliguria, results in identification that is too late to allow successful intervention. New biomarkers are essential to change the dire prognosis of this common condition.

Hypokalemic nephropathy is associated with impaired angiogenesis

Hypokalemic nephropathy is associated with alterations in intrarenal vasoactive substances, leading to vasoconstriction, salt-sensitivity, and progression of interstitial fibrosis. In this study, we investigated whether hypokalemic nephropathy might also involve impaired renal angiogenesis. Sprague-Dawley rats that were fed low-potassium diets developed peritubular capillary loss that began in the inner stripe of the outer medulla (week 2) and progressed to the outer stripe of the outer medulla (week 4) and cortex (week 12). These changes were associated with increased macrophage infiltration, increased expression of both monocyte chemoattractant protein-1 and TNF-alpha, and a loss of vascular endothelial growth factor and endothelial nitric oxide synthase. Renal thiobarbituric acid-reactive substances, markers of oxidative stress, were increased late in disease. In conclusion, hypokalemic nephropathy is associated with impaired renal angiogenesis, evidenced by progressive capillary loss, reduced endothelial cell proliferation, and loss of VEGF expression.

Pathophysiology of salt-sensitive hypertension: a new scope of an old problem

It has been recognized for many years that salt intake is one of the main environmental factors responsible for the development of hypertension. More than 30 years ago, Guyton and co-workers postulated a relationship between blood pressure and natriuresis which maintains sodium balance and extracellular volume; thus an impaired ability of the kidney to excrete sodium requires an increase in blood pressure to increase natriuresis and correct the sodium balance, resulting in hypertension. Currently, the mechanisms responsible for the alterations mentioned above remain under investigation. Among them, microvascular and tubulointerstitial injury induce salt retention and development of salt-sensitive hypertension that appears to be mediated in part by lymphocytes and macrophages infiltrating the tubulointerstitium that produce angiotensin II and stimulate oxidative stress. In the post-angiotensin salt-sensitive hypertension model, angiotensin levels are elevated despite systemic angiotensin II levels being suppressed, and the local angiotensin II levels correlate with the presence of intrarenal inflammation and cortical vasoconstriction. Under these conditions, blockade of the angiotensin II AT1 receptors ameliorate cortical vasoconstriction. Thus, the renal angiotensin system in association with interstitial immune infiltrating cells may play a pivotal role in the development and maintenance of salt-sensitive hypertension.

Proinflammatory and proliferative responses of human proximal tubule cells to PAR-2 activation

Despite the abundant expression of protease-activated receptor (PAR)-2 in the kidney, its relevance to renal physiology is not well understood. A role for this receptor in inflammation and cell proliferation has recently been suggested in nonrenal tissues. The aims of this study were to demonstrate that human proximal tubule cells (PTC) express functional PAR-2 and to investigate whether its activation can mediate proinflammatory and proliferative responses in these cells. Primary human PTC were cultured under serum-free conditions with or without the PAR-2-activating peptide SLIGKV-NH2 (up to 800 microM), a control peptide, VKGILS-NH2 (200 microM), or trypsin (0.01-100 nM). PAR-2 expression (RT-PCR), intracellular Ca2+ mobilization (fura-2 fluorimetry), DNA synthesis (thymidine incorporation), fibronectin production (ELISA, Western blotting), and monocyte chemotactic protein (MCP)-1 secretion (ELISA) were measured. Trypsinogen expression in kidney and PTC cultures was determined by immunohistochemistry and Western blotting. In the kidney PTC were the predominant cell type expressing PAR-2. SLIGKV-NH2, but not VKGILS-NH2, stimulated a rapid concentration-dependent mobilization of intracellular Ca2+ and ERK1/2 phosphorylation and, by 24 h, increases in DNA synthesis, fibronectin secretion, and MCP-1 secretion. These delayed responses appeared to be independent of ERK1/2. Trypsin produced similar rapid but not delayed responses. Trypsinogen was weakly expressed by PTC in the kidney and in culture. In summary, PTC are the main site of PAR-2 expression in the human kidney. In PTC cultures SLIGKV-NH2 initiates proinflammatory and proliferative responses. Trypsinogen expressed within the kidney has the potential to contribute to PAR-2 activation in certain circumstances.

Chronic NOS inhibition actuates endothelial-mesenchymal transformation

Chronic kidney diseases are accompanied by the accumulation of substances like asymmetric dimethylarginine, phenylacetic acid, homocysteine, and advanced glycation end products, known to either inhibit endothelial nitric oxide synthase (eNOS) or uncouple it, consequently limiting the amount of available nitric oxide (NO). Reduced bioavailability of NO induces endothelial dysfunction. An early loss of peritubular capillaries in tubulointerstitial fibrotic areas and injury to endothelial cells have been linked to progressive renal disease. Screening endothelial genes in cells treated with NOS inhibitors showed upregulation of collagen XVIII, a precursor of a potent antiangiogenic substance, endostatin. This finding was confirmed at the level of mRNA and protein expression. Tie-2 promoter-driven green fluorescent protein mice treated with nonhypertensinogenic doses of a NOS inhibitor exhibited upregulation of collagen XVIII/endostatin and rarefaction of capillary profiles. This was accompanied by the increased expression of transforming growth factor-β and connective tissue growth factor in the kidney. Occasional endothelial cells expressed both the marker of endothelial lineage (green fluorescent protein) and mesenchymal marker (α-smooth muscle actin or calponin). In vitro studies of endothelial cells treated with asymmetric dimethylarginine showed decreased expression of eNOS and Flk-1 and enhanced expression of calponin and fibronectin, additional markers of smooth muscle and mesenchymal cells. These cells overexpressed transforming growth factor-β and connective tissue growth factor, as well as endostatin. In conclusion, data presented here 1) ascribe to NO deficiency in endothelial cells the function of a profibrotic stimulus associated with the expression of an antiangiogenic fragment of collagen XVIII (endostatin) and 2) provide evidence of endothelial-mesenchymal transdifferentiation in the course of inhibition of NOS by a pathophysiologically important antagonist, asymmetric dimethylarginine. Both mechanisms may account for microvascular rarefaction.

Angiotensin-induced hypoxia in the kidney: functional and structural changes of the renal circulation

Recent studies emphasize the role of chronic hypoxia in the kidney as a final common pathway to end-stage renal disease (ESRD). Hypoxia of tubular cells leads to apoptosis or epithelial-mesenchymal transdifferentiation. This in turn exacerbates fibrosis of the kidney with loss of peritubular capillaries and subsequent chronic hypoxia, setting in train a vicious cycle whose end point is ESRD. To support this notion, our studies utilizing various techniques such as hypoxia-sensing transgenic rats revealed hypoxia of the kidney in various disease models. While fibrotic kidneys with advanced renal disease are devoid of peritubular capillary blood supply and oxygenation to the corresponding region, imbalances in vasoactive substances and associated intrarenal vasoconstriction can cause chronic hypoxia even at the early phase of kidney disease. Among various vasoactive substances, local activation of RAS is especially important because it can lead to constriction of efferent arterioles, hypoperfusion of postglomerular peritubular capillaries, and subsequent hypoxia of the tubulointerstitium in the downstream compartment. Recent studies using BOLD-MRI showed an immediate decrease of oxygen tension in the kidney after angiotensin II infusion. In addition, angiotensin II induces oxidative stress via activation of NADPH oxidase. Oxidative stress damages endothelial cells directly, causing the loss of peritubular capillaries. Oxidative stress also results in relative hypoxia due to inefficient cellular respiration. Thus, angiotensin II induces renal hypoxia via both hemodynamic and nonhemodynamic mechanisms. While the beneficial effects of blockade of RAS in kidney disease are, at least in part, mediated by amelioration of hypoxia, recent studies have also elucidated the mechanism of hypoxia-induced gene regulation via the HIF-HRE system. This has given hope for the development of novel therapeutic approaches against hypoxia in the kidney.

Angiotensin II, interstitial inflammation, and the pathogenesis of salt-sensitive hypertension

Transient administration of ANG II causes persistent salt-sensitive hypertension associated with arteriolopathy, interstitial inflammation, and cortical vasoconstriction; blocking the vascular and inflammatory changes with mycophenolate mofetil (MMF) prevents vasoconstriction. While infiltrating leukocytes during the salt-sensitive hypertension phase express ANG II, the functional role of ANG II during this phase is not known. We examined the acute effect of candesartan on renal hemodynamics during the established salt-sensitive hypertensive phase and related these findings to direct measurement of intrarenal ANG II and inflammatory cells in rats previously exposed to ANG II with or without MMF treatment. Sham controls were also examined. The administration of ANG II, followed by exposure to high-salt diet, resulted in hypertension, cortical vasoconstriction, an increase in interstitial inflammatory cells (44.8 +/- 1.3 lymphocytes/mm2, and 30.8 +/- 1.2 macrophages/mm2 ANG II vs. 19.6 +/- 2 lymphocytes/mm2, and 22 +/- 0.7 macrophages/mm2 Sham), and increase in renal ANG II levels (1,358 +/- 74.6 pg/ml ANG II vs. 194 +/- 9.28 pg/ml Sham). Treatment with MMF during the administration of exogenous ANG II resulted in reduction in renal interstitial inflammation (19.7 +/- 0.9 lymphocytes/mm2 and 15.9 +/- 0.8 machophages/mm2), ANG II levels (436.9 +/- 52.29 pg/ml), cortical vasoconstriction, and stable blood pressure levels during the subsequent challenge with a high-salt diet. Acute administration of candesartan similarly reduced renal vasoconstriction and blood pressure. We conclude that the cortical vasoconstriction occurring with salt-sensitive hypertension following exposure to ANG II is mediated by intrarenal ANG II, related, at least in part, to the interstitial inflammation.